The invention is directed to a signal generation and correction circuit that includes an LED diode and a photo cell with corresponding inputs and outputs as well as connecting lines leading to current terminals, and to a method for correcting digital signals.
The signals are generated using simple photo transistors and more expensive mask sensors. These produce different output signals, wherein signal generators based on simple photo transistors are not capable of providing accurate signal values in the off-state and when conducting a maximum current.
Due to the ambient radiation and the particular characteristics of timing disks, presently used simple conventional photo transistors with timing disk control always require a minimum operating voltage of at least 0.1 mV, which corresponds to a minimum current of 0.1 xcexcA for a resistance value of 1000 ohm. These values are outside the permissible tolerances for high-performance applications, for example in a computer mouse.
It is therefore an object of the invention to provide a signal generation and correction circuit which produces an output signal of a quality that is at least equivalent to that of mask sensors when using simple photo transistors.
It is further an object of the invention to provide a method for correcting signals which can be used with existing simple photo transistors, in particular in conjunction with timing disks and encoders of conventional design, to produce a constant output signal with small tolerance limits.
The object is solved by the invention in that a Signal generation and correction circuit is provided which includes an LED diode (D1) and a photo-transistor (Q1) which have corresponding inputs and outputs (d1e, d1a and q1e, q1a), as well as connecting lines (1, 2) leading to current terminals (A, B). The inputs and outputs (d1e, d1a) and/or (q1e, q1a) of the diode (D1) and the photo cell (Q1) are connected so as to form a parallel circuit, wherein a resistor (R2) is arranged in the photo-transistor line (3) between the output (q1a) and the node (K) with the connecting line (2) and wherein a resistor (R1) is arranged in the line (2) between the node (K) and the current terminal (B). A transistor (Q2) is connected with its base (q2b) to the output (q1a) or the photo-transistor line (3), whereas the collector terminal (q2c) is connected via a resistor (R3) to the connecting line (1). The collector current has a value of 0 when a photo current flows in the photo transistor (Q1), and whereas a signal with a constant, adjustable magnitude is produced on the emitter side (q2e) of the transistor (Q2) in the absence of a photo current.
Thus, the signal generation and correction circuit of the invention includes an LED diode D1, with the light of the LED diode generating a photo current in a photo transistor Q1 that is connected in parallel with the diode D1. As soon as the photo current flows, the current applied to the collector of the photo transistor Q1 flows through the photo transistor and returns via a resistor R2 via a node to the connecting line 2.
In addition the signal generation and correction circuit may also include that the connecting line (1) is divided into lines (L1) going to the diode (D1), (L2) going to the transistor (Q2) and (L3) going to a photo transistor (Q1), with the output of the photo transistor (Q1) being connected via a line (3) both with the base of the transistor (Q2) as well as via a resistor (R2) with the output of the diode (D1).
In addition, a method for signal generation and/or signal correction is provided, wherein a photo current is produced in a photo transistor (Q1) that is connected in parallel with an LED diode (D1), with photo current capable of controlling the collector current of the photo transistor (Q1) flowing through the connecting lines (1, 2). Here, a transistor (Q2) is connected as a signal generator in parallel with the photo transistor (Q1), wherein the base of the transistor (Q2) is connected with the emitter side of the photo transistor (Q1) and the collector of the transistor (Q2) is connected to the connecting line (1) via a resistor (R3).
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are intended solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.